In North America, Europe and other industrialized areas of the world, vast quantities of fluids, including liquids and gases, are transported through pipelines. These fluids include crude oil, lubricating oil, natural gas, gasoline and so forth. These pipelines are often of considerable length and extend over all types of geographic terrains. Many pipelines today are located underneath rivers and lakes and growing mileages of pipelines are located on the surface of the earth covered by seawater, that is, submerged or subsea pipelines.
Hydrostatic testing of a pipeline may be conducted to verify the structural integrity of the pipeline and to comply with applicable federal and/or state regulations. Conventional hydrostatic testing involves filling and pressurizing the pipeline with water. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. Strength is usually tested by measuring permanent deformation of the pipeline. Hydrostatic testing is the most common method employed for testing pipes and pressure vessels. Using this test helps maintain safety standards and durability of a vessel over time. Newly manufactured pieces are initially qualified using the hydrostatic test.
In natural gas pipelines, hydrostatic testing is extremely important as a catastrophic failure of a natural gas pipeline can result in fires and/or explosions causing significant damage. Unfortunately, natural gas pipelines will contain hydrocarbons in addition to the natural gas such as organic liquids that condense from the natural gas, odorizers for the gas, corrosion inhibitors, and lubricants used in compressors and upstream equipment. When water is used to hydrostatically pressure test a natural gas pipeline, it will be contaminated with such hydrocarbons. These hydrocarbons must be removed from the water before the water can be safely discharged back into streams and rivers.
Many methods for removal of hydrocarbons from waste waters are known and practiced. Among these, the most common techniques are biological remediation, by activated sludge, or aerated lagoons, which are widely practiced by cities and chemical companies to treat waste waters. Other possibilities include adsorption by activated carbon. Unfortunately, biological methods require the liquids be aerated. Aeration would naturally result in volatilization of the lower molecular weight species contained in natural gas. Carbon filtration would require that carbon be regenerated from time to time. This is typically done by heating. Again, the low molecular weight species would be volatilized and potentially escape into the air, unless intentionally captured and scrubbed.